Led lighting source and led lighting apparatus

ABSTRACT

An LED lighting source preventing heat deterioration and improving luminous efficiency includes a mounting substrate having a wiring pattern on a first main surface thereof and a plurality of LED bare chips, each composed of a first semiconductor layer and a second semiconductor layer having respectively different conductivity, an active layer disposed therebetween, and a metal electrode on the first semiconductor layer and substantially equal in area thereto, and each LED bare chip being joined to the wiring pattern according to flip chip mounting of the metal electrode to form a junction between the wiring pattern and the metal electrode. Each junction is formed so that an area thereof is at least 20% of the area of the metal electrode. Thermal resistance from the active layers through to a second main surface of the mounting substrate, which is a back surface thereof, is set to 3.0 9C./W or lower.

TECHNICAL FIELD

The present invention relates to an LED module used in an LED lightingsource or an LED lighting apparatus, and in particular to a techniquefor improving thermal dissipation properties.

BACKGROUND ART

LED lighting sources which use LEDs (Light Emitting Diodes) arereceiving attention as the next generation of light sources. Unlikegeneral, conventional light sources, LEDs have the advantage of having along life, as well as being able to be made extremely thin and compact.For this reason, LEDs are superior in that they present relatively fewrestrictions in terms of installation position, and therefore highexpectations are held that LEDs will be able to be used for a wide rangeof applications.

As one specific example of an LED lighting source, an LED module hasbeen developed in which plurality of LED bare chips are mounted denselyon a substrate, and the surface of the LED bare chips is covered withtransparent resin. Such an LED module is disclosed in Japanese PatentApplication Publication No. 2003-124528.

LED lighting apparatus of various shapes and light outputs can beachieved by using one or multiple LED modules having the describedstructure, with each LED module being removably held by a socket orconnector and power being supplied thereto.

However, since the aforementioned LED module uses LED bare chips as thelight source, a relatively large amount of power must be suppliedthereto. Specifically, in order to increase the luminous flux of eachLED bare chip as much as possible, it is necessary to supply current toeach LED bare chip that is greater than current in ordinary use otherthan lighting (for example, for light emission display). As one example,if the LED bare chips have a 0.3 mm square, and the current in ordinaryuse is approximate 20 mA, the current density of the active layer isapproximately 222.2 mA/mm², and to increase luminous flux, ifovercurrent (maximum current) is approximately 40 mA, current density inthe active layer is approximately 444.4 mA/mm².

While supplying a large current as described above achieves a high lightoutput from the LED bare chips during driving, the temperature of theLED bare chips mounted on the substrate (also called junctiontemperature) rises considerably. Generally, one property of LED barechips is that being placed in a state of high temperature has a greateffect on life span. For example, the life span of an LED lightingapparatus in which LED bare chips are used is thought to be reduced byhalf if, at room temperature, the temperature of the LED bare chipsincreases by 10° C. Furthermore, being in a high temperature statecauses a problems of thermal deterioration and reduces the luminousefficiency (light usage efficiency).

For these reasons, in order to maintain the luminous efficiency of lightsources of LED lighting such as LED modules, heat must be dissipatedsuch that the mounted LED bare chips do not reach a state of excessivelyhigh temperature.

Furthermore, in LED lighting apparatuses that use LED modules, heat thatoccurs during driving is intended to be dissipated outside mainly fromthe back surface of the LED modules. For this reason, in LED lightingapparat uses, a structure in which a heatsink is provided in closethermal contact with the back surface of each LED module is employed.However, the heat dissipating effect of such heatsinks is presently notbeing used to its full potential, and there is still much room forimprovement.

DISCLOSURE OF THE INVENTION

In view of the stated problems, the object of the present invention isto provide an LED lighting source, such as an LED module, that hassuperior performance by preventing deterioration of LED bare chips andimproving luminous efficiency, and an LED lighting apparatus that usesthe LED lighting source.

In order to solve the stated problems, the present invention is an LEDlighting source including: a mounting substrate having a wiring patternon a first main surface thereof; and a plurality of LED bare chips, eachcomposed of a first semiconductor layer and a second semiconductor layerthat have respectively different conductivity, an active layer disposedbetween the first and second semiconductor layers, and a metal electrodedisposed on the first semiconductor layer and being substantially equalin area to the first semiconductor layer, and each LED bare chip beingjoined to the wiring pattern according to flip chip mounting of themetal electrode to form a junction between the wiring pattern and themetal electrode, wherein each junction is formed so that an area thereofis at least 20% of the area of the metal electrode, and thermalresistance from the active layers through to a second main surface ofthe mounting substrate, which is a back surface thereof, is set to 3.0°C./W or lower.

According to the LED lighting source of the present invention having thestated structure, the junction area of the wiring and the metalelectrode, which is substantially equal in size to the area of the firstsemiconductor layer of the LED bare chip, is set so as to be at least20% of the first semiconductor layer that opposes the wiring. Inaddition, the thermal resistance from the active layer through to backsurface of the mounting substrate of the LED bare chip is set so as tobe no more than 3.0° C./W. According to the stated structure, thermalconductivity from the active layer to the substrate side is improved,the temperature of the LED bare chip during driving is kept to 80° C. orlower, and the excessive temperature rises can be avoided. As a result,thermal deterioration of the LED bare chip is prevented, and the LEDlighting source can be driven favorably, maintaining luminousefficiency.

Here, at least the metal electrodes and the wiring pattern may be joinedaccording to one of a gold-gold junction, a gold-aluminium junction, anda gold-tin junction.

Furthermore, each junction may be made up of two or more bumps.

Specifically, each junction may be made up of two or more bumps thateach have a diameter of at least 100 μm, or three or more bumps thateach have a diameter of at least 80 μm.

In such an LED bare chip, it is preferable that current density of theactive layer of each LED bare chip during driving is in a range of 250mA/mm² to 660 mA/mm² inclusive.

Furthermore, the mounting substrate may be composed of an insulationlayer and a metal layer, the first main surface on which the wiringpattern is disposed being a main surface of the insulation layer, andthe second main surface of the mounting substrate, which is an oppositesurface to the surface on which the wiring pattern is disposed, being asurface of the metal layer.

Here, the mounting substrate may include an insulation layer that iscomposed of a composite material that includes an inorganic filler and aresin composite.

Alternatively, the mounting layer may include an insulation layer thatis composed of a ceramic material.

Furthermore, the mounting substrate may be composed of a ceramicmaterial. In this case, the ceramic material may include at least one ofAlN, Al₂O₃, and SiO₂.

Furthermore, the present invention is an LED lighting apparatusincluding the stated LED lighting source, wherein the LED lightingapparatus includes a heatsink that is provided in close thermal contactwith the back surface of the mounting substrate, and that has a thermalresistance of no less than 1.0° C./W and no greater than 4.° C./W.

Furthermore, the present invention is an LED lighting apparatusincluding the stated LED lighting source, wherein the LED lightingapparatus includes a heatsink that is provided in close thermal contactwith the back surface of the mounting substrate, and that has anenveloping volume of 100 cm³ to 820 cm³, inclusive.

Note that the heatsink may be composed of at least one material chosenform the group consisting of Al, Cu, W, Mo, Si, AlN, and SiC.

In the present invention, even if the LED bare chip growth substrate hasa conventional structure, such as sapphire, SiC, GaN or AlN, since theheat from the active layer is directly dissipated through the firstsemiconductor layer, the LED bare chip temperature can be adjustedsimply by setting the junction area with the wiring. This isadvantageous in that the present invention can be realized relativelysimply using a conventional manufacturing method. The fold bumps andmetal have high heat dissipating properties, and therefore areadvantageous in adjusting thermal resistance.

Furthermore, in the LED lighting apparatus of the present invention thatused the LED lighting source with the stated structure, heat from theLED lighting source is effectively dissipated due to a heatsink having athermal resistance of 4.0° C./W or lower being provided in close thermalcontact with the back surface of the substrate of the LED lightingsource. By using heatsink with such heat dissipating characteristics,the temperature of the LED bare chips during driving can be kept to 80°C. or below. This enables luminous efficiency to be maintained whileprevention heat deterioration of the LED bare chips, and an LED lightingapparatus with favorable performance to be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the structure of an LED card in a first embodiment;

FIGS. 2A and 2B show examples of a substrate wiring patterns;

FIGS. 3A and 3B show the substrate circuit structures;

FIG. 4 shows the structure an LED device and its surroundings;

FIG. 5 shows the structure of an LED device and its surroundings;

FIG. 6 shows an LED bare chip mounting structure;

FIG. 7 is a graph showing the relationship between ambient temperatureand forward current characteristics of a general LED bare chip;

FIG. 8 is a graph showing the relationship between bare chip temperatureand thermal resistance;

FIG. 9 is a graph showing the relationship between the p electrode areaoccupied by the junction area (G1 and G2 spot area) and the junctiontemperature Tj;

FIGS. 10A and 10B show the structure of an LED lighting apparatus of asecond embodiment;

FIGS. 11A and 11B are cross sectional diagrams showing the structure ofthe LED lighting apparatus;

FIG. 12 is a graph showing the relationship between bare chiptemperature and heatsink thermal resistance;

FIG. 13 is a graph showing the relationship between bare chiptemperature and heatsink enveloping volume;

FIG. 14 is a graph showing the relationship between bare chiptemperature and heatsink area;

FIG. 15 is a graph showing the relationship between bare chiptemperature and heatsink weight;

FIGS. 16A and 16B show structures of LED lighting apparatuses asvariations;

FIGS. 17A, 17B and 17C show examples of structures of heatsinks asvariations;

FIG. 18 shows an alternative structure of an LED card; and

FIG. 19 shows another alternative structure of an LED card.

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment>

1-1. Overall Structure of Card-Type LED Module

FIG. 1 is a perspective view showing the overall structure of acard-type LED module 1 (hereinafter called “LED card 1”) of the firstembodiment.

The LED card 1 is roughly composed of a substrate 10, an LED lightsource unit 30 formed on the surface of the substrate 10 (the surface ofan insulation layer 10 b), and power supply terminals 20 a to 20 h.

The substrate 10 is made of a highly thermally distributive metalcomposite (here, a aluminium composite) and is composed of a circuitformation unit (insulation layer) 10 b and a metal layer 10 a. Oneexample of the size of the substrate 10 is 28.5 mm (depth) by 23.5 mm(width) by 1.2 mm (height). The circuit formation unit 10 b is a 0.2mm-thick mounting surface made of a mixture of a resin composite and aninorganic filler. The metal layer 10 a is aluminium or the like with athickness of 1.0 mm. The overall thickness of the substrate 10 ispreferably at least 0.7 mm from a point of view of heat dissipationcharacteristics and mechanical strength during driving, and no more than2.0 mm for ease of cutting the substrate. Note that the overall shape ofthe substrate 10 may be varied appropriately according to conditionssuch as the number of LED devices 300 to be mounted, and the substrate10 is not limited to the described size.

The inorganic filler is preferably at least one type selected from thegroup consisting of Al₂O₃, MgO, BN, SiO₂, SiC, Si₃N₄, and AlN.Furthermore, to achieve a high filling rate and heat conductivityproperties, it is preferable that the particles of the inorganic fillerare grain-shaped, and particularly preferable that the particles arespherical. The resin composite preferably includes at least one typeselected from the group consisting of epoxy resin, phenol resin, andcyanate resin. In addition, the resin composite is preferably formedfrom a mixture of 70% to 95% of the inorganic filler and 5% to 30% ofthe resin composite.

Note that a ceramic material may be used for the insulation layer 10 b.If a ceramic material is used, it is preferable that the ceramicmaterial includes at least one type from the group consisting of MgO,CaO, SrO, BaO, Al₂O₃, SiO₂, ZnO, TiO₂, NiO, Nb₂O₃, CuO, MnO, and WO₃.

The metal layer 10 a may be fabricated from aluminium, copper, iron,stainless steel, or an alloy of any of these. In terms of heatdissipating properties, copper, aluminium, iron and stainless steel, inthe stated order, are superior. On the other hand, in terms of heatexpansion rate, iron, stainless steel, copper, and aluminium, in thestated order, are superior. Furthermore, in terms of ease of use, suchas in rust prevention processing, an aluminium material is preferable,and in terms of avoiding reliability deterioration caused by heatexpansion, iron or stainless steel is preferable. In this way, anappropriate material may be selected according to needs. Furthermore, bysubjecting the surface of the metal layer 10 a to insulation processing,short circuits caused by the metal layer 10 a touching the wiring 200and 201 or the like can be prevented. Examples of such insulationprocessing include electrolytic polishing, andodizing, electrolessplating, and electrodeposition.

Note that the back surface of the metal layer 10 a is flat in order toachieve a high heat conductivity rate, under the assumption that heatdissipating means such as a heatsink will be provided in close thermalcontact with the back surface.

Furthermore, although the substrate 10 is described as having astructure in which the metal layer 10 a and the insulation layer 10 bare layered together, a ceramic substrate may instead be used in thepresent invention. In such as case, it is preferable to use a materialthat includes at least one of AlN, Al₂O₃, and SiO₂ which have relativelyhigh thermal conductivity.

1-2. Substrate Wiring

Upper layer wiring 200 of Cu foil in a pattern shown as shown as anexample in FIG. 2A is formed on the surface of the insulation layer 10b. The surface of this upper layer wiring 200 is plated with Ni—Au. Inthe pattern in the drawing, patterns 201A, 201B, and so on, which areisolated from and independent of each other, are provided successively,and an LED bare chip 2 is mounted according to flip chip junction ineach of opposing parts between each two adjacent patterns (for example,201A and 201B) in the lengthwise direction of the substrate (thevertical direction in the drawing). An area 20A in FIG. 2A indicates aspecific LED bare chip mounting area.

Furthermore, the power supply terminals 20 a to 20 h are disposed at oneend of the upper layer wiring 200. The power supply terminals 20 a to 20h are connected to external terminals, and are for supplying power tothe LED to 300. It is preferable to use a socket or a connecter to holdthe LED 1 when the power supply terminals 20 a to 20 h are connected tothe external terminals. Here, “socket” and “connector” refer to amaterial or component in which the LED card 1 of the present embodimentis able to be detachably mounted in order to achieve an electricalconnection. The LED card 1 can be driven with use of a conventionalsystem for electrical connection if the size of the LED card 1 is madeto suit specifications of a socket or connector for an existing memorycard or the like.

The number of the power supply terminals 20 a to 20 h and the positionalrelationship thereof on the insulation layer 10 b are not limited tothose described, however the pitch of adjacent terminals shouldpreferably be maintained at least 0.8 mm in order to prevent shortcircuits.

Lower wiring 201 made of Cu foil in the pattern shown in FIG. 2B isprovided internally in the insulation layer 10 b. The lower wiring 201has linear patterns 201 a to 201 h and is arranged so as toappropriately connect the upper wiring 200. The upper wiring 200 and thelower wiring 201 are mutually connected inside the insulation layer 10 bthrough connection vias 21 and 22.

According to this kind of wiring 200 and 201, in the first embodiment, aseries-parallel circuit made up of LED to 300 shown in FIG. 3A isformed. Note that the structure of the circuit is not limited to thatdescribed, and may use numerous parallel connection of LED to 300 asshown in FIG. 3B.

1-3. Structure of the LED Light Source Unit

An LED light source unit 30 shown in FIG. 1 is the principalcompositional device of the LED card 1, and is mounted with high densityas a lighting-use light source, not as a conventional display-use lightsource or the like. As one specific example, 8 by 8 (64 in total) LED to300 of a diameter of 2 mm at set intervals on the main surface of theinsulation layer 10 b, arranged in a square shape having a 20 mm squaresize. As one example of specifications, a forward direction current of40 mA and a forward direction voltage of 120 V achieve a luminous outputof 1201 m during driving at a room temperature of 25° C. (measurementconditions for light output of general lamps for lighting determined byJIS standard). The overall height of the LED card 1 to the LED lightsource unit 30 is 3 mm.

Note that the number of LED to 300 and the pattern in which they arearranged are not limited to the described example.

The structure of the LED device 300 and its surrounds is as shown in anenlarged cross-sectional view in FIG. 4.

First, an aperture is formed in an aluminium optical reflecting plate301 that is to act as a frame, so as to have a diameter of 2 mm and aconical reflection surface 301 a. The optical reflecting plate 301 isthen laminated on the surface of the insulation layer 10 b.

The LED bare chips 2 are formed, as one example, in a square shapehaving a 0.32 mm square. Each LED bare chip 2 has a structure in whichon a lower surface of a device substrate 401 that is sapphire a GaNsecond semiconductor layer (called an n-type semiconductor layer) 402,an active layer 403, a first semiconductor layer (called a p-typesemiconductor layer) 404 are layered downward in the stated order.Furthermore, an n-type semiconductor layer electrode (called an nelectrode) 406 and a p-type semiconductor electrode (called a pelectrode) 405 are layered on the n-type semiconductor layer 402 and thep-type semiconductor layer 404, respectively. The p electrode 405 has ametal surface, and here the p electrode 405 is encompasses the wholelower surface of the p-type semiconductor layer 404. During driving,light is emitted principally at the surface of the active layer 403.

The LED bare chip 2 having this structure is obtained by successivelylayering a GaN n-type semiconductor layer and a p-type semiconductorlayer on a sapphire substrate with a diameter of approximately 2 inches,according to a CVD method or the like, and then subjecting the formedsemiconductor wafer to dicing processing. Instead of sapphire, SiC orGaN may be used for the device substrate 212.

Note that when the LED bare chip 2 is to emit near-ultraviolet light, orblue or green (blue-green) light (light with a relatively shortwavelength), it is possible to provide a light emitting layer on thesapphire device substrate 401. Since near-ultraviolet light, and blue orgreen light pass thorough the sapphire device substrate 401, the lightemitting layer may be provided either on the upper surface or the lowersurface of the device substrate 401.

In this way, each LED bare chip 2 has a structure in which semiconductorlayers 402 and 403 are disposed on the lower surface of the devicesubstrate 401. These semiconductor layers 402 and 403 are used to flipchip (FC) mount the p electrode 405 and the n electrode 406 of the LEDbare chip 2 by gold bumps G1, G2, G3 in the aperture in the opticalreflection plate 301 with respect to the patterns 201A and 201B in theupper wiring 200 on the surface of the insulation layer 10 b. Themounting of the LED bare chip 2 is described in detail later.

Note that although the gold bump G3 is shown in FIG. 4 as being largerthan the other gold bumps G1 and G2, this is because the gold bump 3 isshown as being taller in the thickness direction of the LED bare chip 2semiconductor layers in order to ease comprehension or the structure ofthe LED bare chip 2. In reality, the gold bumps G1, G2 and G3 differ byno more than several tens of nm in the thickness direction. Furthermore,although the gold bumps G1, G2 and G3 are shown as being substantiallycircular, in reality they are not necessary perfectly circular, but maybe elliptical, for example.

Performing flip chip mounting as described eliminates the need, whichexits in conventional shell-type LED devices and the like, to providewires for power supply in the LED devices, and therefore eliminates theneed for areas for wire bonding. This enables the interval between eachadjacent pair of LED bare chips 2 to be made narrower, and the LED chips2 to be mounted with higher density. An advantage of such high-densitymounting is that it enables adjustment of colors in display in whichmultiple LED bare chips 2 (or bare chips) of differing colors are used.Furthermore, since wires are unnecessary, the problem of the wiresblocking light during driving is fundamentally solved.

Silicone resin or epoxy resin is placed in the aperture so as toencapsulate the LED bare chip 2 and overflow slightly from the aperture,and is molded into a resin lens 302 having a predetermined shape such asa convex shape or a semispherical shape. Note that phosphor of a desiredcolor may be dispersed in the resin lens 302.

Such a structure of the LED device 300 and its surrounds is the same foreach of the 64 LED to 300 in the LED light source unit 30.

FIG. 5 shows an example of a structure in which phosphor 407 is disposedso as to encapsulate the LED bare chip 2, and the resin lens 302 isformed so as to cover the optical reflecting plate 301. The LED barechip of the present invention may have this structure.

1.4 Mounting of the LED Bare Chip

FIG. 6 is a schematic drawing of the LED bare chip 2 as seen fromunderneath, for describing the junction area in more detail.

As shown in FIG. 6, in the first embodiment, the flip chip mounting(specifically, the n electrode 406 is joined to the upper layer wiringpattern 201A with the one gold bump G3, and the p electrode 405 isjoined to the upper wiring 201B with the two gold bumps G1 and G2, usinggold-gold bonding) is performed specifically by placing the gold bumpsG1, G2 and G3 on the upper layer wiring patterns 201A and 201B, placingthe LED bare chip thereon, and applying ultrasonic waves.

Here, as a characteristic of the first embodiment, the total area of thegold bumps G1 and G2 provided with respect to the p electrode 405between the p electrode 405 whose surface is metal and the mountingpattern 201B is set so as to be no less than 20% of the area of the pelectrode 405 that is substantially equal in area to each of the p-typesemiconductor layer 404 and the active layer 403. Note that grounds for20% of the area of the p electrode 405 are described later. In order toachieve this area ratio, the spot diameter of each of the gold bumps G1and G2 is at least 100 μm. The diameter was set in this way as a resultof the inventors investigating heat-dissipation design of the LED card1, and discovering that if the respective spot diameters of the goldbumps G1 and G2 are at least 100 μm, when the LED card 1 is driven witha maximum current of 50 mA, thermal resistance of the substrate 10(hereinafter called “substrate 10 thermal resistance”), specificallythermal resistance in the distance corresponding to the “Junction toPackage” of the LED bare chips 2 (thickness direction from the activelayer 403 of the LED bare chip 2 to the back surface of the metal layer10 a), can be suppressed so as to be no greater than 3.0° C./W. Notethat in the present invention, thermal resistance does not denote avalue relating to individual LED bare chips, but denotes a valuerelating to all bare chips when the LED card 1 is driven with all inputpower. In the present embodiment, thermal resistance is the thermalresistance relating to all input power that drives the chips in 64places as shown in FIG. 1. In other words, the present invention can beapplied even when the embodiment differs from the present embodiment isaspects such as LED chip size, LED chip count, and LED chip shape. Inthis way, in the first embodiment, by setting the substrate 10 thermalresistance to be no greater than 3.0° C./W by setting the diameters ofthe gold bumps G1 and G2, when heat dissipating means (heatsink) hasbeen thermally attached to the metal layer 10 a of the substrate 10, thetemperature (junction temperature) of the LED bare chips 2 duringdriving is kept to 80° C. or lower.

Note that a number of examples can be given of a structure in which themetal layer 10 a of the substrate 10 and the heat dissipating means areprovided in close thermal contact. For example, other structures besidesone in which the metal layer 10 a and the heat dissipating means arephysically in direct contact with each other, include one in which themetal layer 10 a and the heat dissipating means are physically in directcontact with each other via heat conducting means such as a siliconeheat dissipating sheet, silicone rubber, silicone grease, or a heatpipe. Another example is a structure in which the metal layer 10 a andthe heat dissipating means are provided with a set distancetherebetween, and thus without directly contacting each other, via sucha heat conducting means. In the present invention, a structure thatachieves “close thermal contact” may include the described structures,and is defined as a structure that achieves an effect of dissipatingheat from the metal layer 10 a of the substrate 10 via the heatdissipating means.

That is to say, conventionally, bumps in flip chip mounting are simplyused as connection means between the mounted devices and the wiring.However, in fabricating the LED card 1, the present inventors focused onheat dissipating properties of gold bumps in relation to directhigh-density mounting of the LED bare chips 2 on a highly heatdissipating substrate using flip chip mounting. In this way, the LEDcard 1 is designed to reduce thermal resistance of the substrate 10during driving. In other words, the inventors have discovered therelationship between the gold bump junction area and the LED bare chipjunction temperature in direct mounting of LED bare chips on a highlyheat dissipating substrate.

1.5 Effects During Driving

The LED card 1 having the stated structure is mounted in a socket or aconnector for usage. At this time the power supply terminals 20 a to 20h contact the external terminals provided on the socket or theconnector. Furthermore, a heatsink (not illustrated) is mounted on theback surface of the LED card 1 (the surface of the metal layer 10 a) soas to be in close contact thermally therewith. It is preferable that thethermal resistance of the heatsink be as low as possible.

If a predetermined power is supplied to the LED card 1 in this state,power is supplied to the bare chips 2 of the LED light source unit 30.This causes the LED bare chips 2 to emit light primarily in the activelayer 403. The light is reflected by the cone-shaped reflective surface301 a in the aperture 31 of the aluminium optical reflecting plate 301,and effectively extracted from the from the front surface. The light isfurther converged by the resin lens 302, and used as a lighting sourcehaving a sufficient light output of 1201 m.

Furthermore, at this time heat generated in the LED bare chips 2 isdissipated outside, principally through the substrate 10 via the highlyheat conductive metal layer 10 a.

Here, in the first embodiment the diameter of the gold bumps G1 and G2in the p electrode 405 is set so as to be no less than 100 μm, and thetotal area (junction area) of the gold bumps G1 and G2 is set so as tobe no less than 20% of the area of the p-type semiconductor layer 404that opposes the insulation layer 10 b via the p electrode 405. Indetail, if the bare chip has a 0.32 mm square, the area of the p-typesemiconductor layer 404 is expressed as 0.32 (mm)*0.32(mm)*75(%)=0.0768(mm²). Therefore, when the bump diameter is 100 μm andtwo bumps are provided, the junction area is 0.0157 mm², and the bumpsoccupy approximately 20% of the area of the p-type semiconductor layer404. According to such settings, the thermal resistance between surfaceof the active layer 403 and the metal layer 10 a (the substrate 10thermal resistance), which corresponds to the junction to package of theLED bare chip 2, is kept to 3.0° C./W or below.

By keeping the thermal resistance of the substrate 10 to no greater than3.0° C./W in this way, the temperature of the LED bare chips 2 duringdriving time of the LED card 1 of the present embodiment is suppressedto be no more than 80° C., and an effect of suppressing excessive heatgeneration in the LED bare chips 2 is achieved. Generally it isundesirable for the temperature of LED bare chips to exceed 80° C.because such high temperature causes deterioration in performance of theLED bare chips and reduction of luminous efficiency (grounds for thistemperature are described in detail later). However, since thetemperature of the LED bare chips 2 is suppressed to be no greater than80° C. in the first embodiment, the LED bare chips 2 can be driven in adesirable, stable manner without the temperature reaching a hightemperature of over 80° C.

Furthermore, in the first embodiment, the thermal resistance of thesubstrate 10 can be adjusted according to the area of the bumps (goldbumps G1 and G2) in flip chip mounting, and therefore the LED card 1 hasan advantage of being able to be manufactured relatively simply using aconventional method.

Note that although an example using two bumps (gold bumps G1 and G2) isgiven in the first embodiment, the number of bumps may be three or more.In such a case, if three bumps having respective diameters of 80 μm areprovided, the junction area will be 0.015072 m², and if four bumpshaving respective diameters of 70 m are provided, the junction area willbe 0.015386 mm². In both cases, the bumps will be approximately the samein area as the metal p-electrode 405 and the p-type semiconductor layer404, and will occupy approximately 20% of the area of the active layer403.

Note that it is even more preferable for the junction area to occupy 30%or more of the area of the active layer 403 that has substantially thesame area as the metal p electrode 405 and the p-type semiconductorlayer 404. Furthermore, a material other than metal may be used for thebumps, but metal is preferable in terms of heat conductivity.

Furthermore, the same effect can be obtained if the LED bare chips havea 0.32 mm square by making the junction area at least 20% with respectto the metal p electrode having substantially the same area as thep-type semiconductor layer and the active layer. In addition, if thebumps area positioned separate from each other so that the junction areais dispersed over the surface of the p electrode, effects can beobtained of spreading heat throughout the p electrode and dissipatingheat favorably from the active layer of the LED bare chip.

Bumps (solder bumps or gold) only, or the bumps together with anothermetal material (for example, a junction-use adhesive that includes metalparticles) may be used to connect the LED bare chips to the wiring side.Alternatively, an alloy connector or a solder connector, of whichgold/tin is representative, may be used to connect the LED bare chips tothe wiring side. However, the inventors found through experiments thatit is preferable to use gold bumps in performing conventional flip chipmounting processing because they contribute effectively to setting thethermal resistance, as well as high mounting efficiency, mountingjunction reliability, and stress easing.

Furthermore, it is not necessary to have a structure that usesspot-shaped bumps. As one alternative structure, the junction may beformed by a junction area that covers the whole p electrode 405 (inother words, an area ratio of 100% with respect to the metal p electrodebeing substantially equivalent in area to the p-type conductive layerand the active layer).

FIG. 19 shows an example of an alternative embodiment of a solderjunction in which a light emitting layer is provided on the lower sideof the LED bare chip in the same way as a flip chip.

In FIG. 19, an LED bare chip has a structure in which the GaN secondsemiconductor layer (n-type semiconductor layer) 402, the active layer403, and the first semiconductor layer (p-type semiconductor layer) 404are layered downward in the stated order on the lower surface of adevice substrate 413 made from SiC, and, in addition, the n electrode406 is provided on the SiC element substrate 413, and the p-typeelectrode 405 is provided on the p-type semiconductor layer 404. Here,gold-tin alloy is one example of the material that may be used for theelectrodes 405 and 406. During driving, light is emitted principally inthe active layer 403.

A light emitting layer provided in this way on the lower side of the LEDbare chip allows heat to be dissipated highly effectively.

Furthermore, a favorable heat dissipation effect can also be obtainedwith a solder junction.

Note that another type of conductive substrate, such as a GaN substrate,may be used for the element substrate of the LED bare chip.

1-6. Grounds for the Numerical Range Specified in the Present Invention

General thermal properties of the LED bare chips are disclosed, forexample, in the graph show in FIG. 7 which shows ambient temperature andforward current properties of the LED bare chips (Panasonic DATA BOOK2000 “Hikari Handotai Soshi Kashi Hakko Diode Unit Shohinhen” (“OpticalSemiconductor Devices, Visible Light Emitting Diodes, Unit Products”)).

The graph in FIG. 7 shows the amount of forward current that isappliable in a general LED bare chip when an ambient temperature Ta isincreased. A rise in the ambient temperature is accompanied by a rise inthe temperature of the LED bare chip. As shown by the graph, when theambient temperature reaches 80° C. to 85° C., the LED generatesexcessive heat, and deterioration of the device advances extremely. Forthis reason, 80° C. is thought to be the maximum heat generatingtemperature at which sufficient power is supplyable to LED bare chips.Consequently, if the temperature of the LED bare chip exceeds 80° C.,this temperature rise becomes a restriction, and sufficient power is nolonger able to be supplied to the LED bare chip. Furthermore, if thetemperature exceeds 80° C., the sealing resin of the LED bare chipbegins to exhibit considerable heat deterioration. For this reason, inaddition to incurring a reduction in luminous efficiency, the LED barechip itself is also thought deteriorate due to the heat, as describedabove.

Taking the described thermal properties into account, the presentinventors performed experiments to measure the temperature in LED barechips when the power input to the LED bare chips was set at 40 mA andthe resistance of the substrate was varied. When a large current thatexceeds the current density 260 mA/mm² of a general size LED bare chipis applied and a large luminous flux is to be obtained, the luminosityamount reaches saturation due to the carrier overflow in the area inwhich large current whose density exceeds approximately 660 mA/mm², evenif the temperature of the LED bare chips is maintained close to roomtemperature, and markedly increased defects occur in the epilayer ofdevices during operation. This causes a reduction in lifespan.

The experiment results are shown in the graph in FIG. 8, which indicatesthe relationship between bare chip temperature and heats ink thermalresistance. In this experiment, a heatsink was provided so as to be inclose thermal contact with the metal layer of the LED card, and thethermal resistance of the heatsink was varied.

As can be seen from the graph in FIG. 8, when the LED bare chips aredriven under the conditions of an ambient temperature prior to drivingof 35° C. (this temperature being close to body temperature and thoughof as the value of the upper limit of room temperature in a livingspace), a forward current of 40 mA, and a making current of 10 W, andwhen the thermal resistance of the heatsink is extremely low(specifically, 1° C./W), if the thermal resistance of the substrate is3° C./W or less, the LED bare chip temperature can be kept at 80C orlower.

Consequently, when actually driving the LED card 1 using the heatdissipating effect of the heatsink, stable driving, without causingexcessive rise in the temperature of the LED bare chips, can be said tobe possible if the thermal resistance of the substrate is 3° C./W orlower.

The reason for using 1° C./W as a reference for the heatsink thermalresistance as in FIG. 8 when measuring the thermal resistance of thesubstrate is as follows.

Specifically, if thermal resistance of the heat dissipating means(heatsink) is decreased, the volume (enveloping volume) thereofincreases. It is preferable for the thermal resistance of the heatdissipating means to be low, in other words, for the enveloping volumeof the heat dissipating means to be high, because this increases heatdissipating performance. However, in reality, there is a limit to thesize of the heatsink when the LED card 1 of the present invention isincorporated into an LED lighting apparatus as a light source.

The size of room-use lighting sources currently on the market can beused as a reference for a specific size of a usable heatsink. Forexample, in the “Parukku Ball G-Type Series” which is relatively-largein size among bulb-type fluorescent lamps by Matsushita ElectricalIndustrial Co., Ltd., an example of the size of the heatsink is an outerdiameter of 90 mm, a length of 130 mm, and a volume of approximately 830cm³ when measured as the volume of an approximately cylindrical shape.

Here, Table 1 shows data that includes the relationship between theenveloping volume of the heatsink and the heatsink thermal resistance.In Table 1, “Heatsink No.” refers to a number given to at sink preparedas a sample. The heatsink numbers were assigned at the larger thenumber, the lower the enveloping volume. TABLE 1 Relationship BetweenHeatsink and Junction Temperature (Ambient Temperature: Ta = 25° C.)Thermal Resistance Enveloping Junction Temperature (° C.) Heatsink (10W) Volume 20 30 40 50 No. ° C./W cm³ mA mA mA mA 1 0.38 4464 34.8 38.741.7 44.5 2 0.56 2322 35.2 39.0 43.3 46.8 3 0.65 1108.8 35.8 41.8 46.750.3 4 1.0 816 36.5 42.8 48.3 52.8 5 1.24 571.2 38.5 44.4 51.5 55.0 61.7 400 39.5 46.1 52.3 57.7 7 1.9 280 41.2 48.7 56.5 62.3 8 2.2 208 43.252.9 61.4 69.7 9 2.6 145.6 46.1 57.6 66.8 74.2 10 2.9 144.06 44.1 56.065.6 73.8 11 3.3 104 47.2 56.8 64.5 74.8 12 3.4 108.78 46.8 59.3 69.078.0 13 3.9 100 47.6 60.3 69.5 79.5 14 4.3 73.5 47.2 64.4 70.8 81.3 154.5 59.5 53.2 57.5 69.8 82.5 16 5.2 52.5 51.3 69.0 78.5 86.4 17 5.6 42.552.6 68.6 92.0 Junction Temperature (° C.)

As can be seen from the data for heatsink No. 4 in Table 1, when theenveloping volume is 816 cm³, the thermal resistance is 1.0° C./W. Thethermal resistance can be lowered if the enveloping volume is increased,however, heatsink No. 4 is suitable in terms of size because its volumeis approximately 830 cm³ when considered as a cylindrical shape, andtherefore can be incorporated in a lighting apparatus in reality.Consequently, a heatsink having the size of No. 4 and the thermalresistance of 1.0° C./W is thought to be appropriate as a reference fora realistic heatsink. For this reason, 1.0° C./W is used as a referencefor heatsink thermal resistance in FIG. 8.

Note that when the LED bare chips 2 in the LED card 1 of the presentinvention are formed in a square shape with a 0.32 mm square, the areaof the active layer 403 is substantially the same as the area of thep-type semiconductor layer 404, and, as one example, occupies 75% of thearea of the LED bare chip 2. Therefore, the area of the active layer canbe expressed by an expression 0.32 (mm)*0.32 (mm)*75(%)=0.0768 (m²).Based on this expression, the current density in the active layer 403when forward currents of 20 mA, 30 mA, 40 mA, and 50 mA, respectively,are applied to the LED bare chips 2 during driving will be 260 mA/mm²,390 mA/mm², 521 mA/mm², and 651 mA/mm². Here, particularly when applyinga forward current of 50 mA to the LED bare chips 2, the temperature ofthe LED bare chips 2 may exceed 80C if a heatsink having an enveloping(external dimensions)volume of 100 cm³ and thermal resistance ofapproximately 4.0° C./W is used as the heat dissipating means providedin close thermal contact with the metal layer 10 a of the LED card 1.

Furthermore, sufficient luminous flux for use as a lamp cannot beobtained if the forward current is below 20 mA (a current density of 250mA/mm² in the active layer 403).

For these reasons, the appropriate range for the current density in theactive layer 403 of the LED bare chips 2 of the present invention isthought to be 250 mm² to 660 mA/mm².

FIG. 9 is a graph showing the relationship between junction area of thep-type semiconductor layer of the LED bare chip (specifically, thejunction area (the spot area of Gland G2) occupying the p electrode areahaving the same area as the p-type semiconductor layer) and the junctiontemperature Tj, under a set condition of the substrate thermalresistance being 3° C./W or 2° C./W.

As is clear from FIG. 9, the junction area and the junction temperatureTj are inversely proportionate, and in order to keep the junctiontemperature to 80° C. or below, it is necessary for the junction area tooccupy at least 20% of the p-type semiconductor layer when the thermalresistance is 3° C./W. This data forms the grounds for setting the totalarea of the gold bumps G1 and G2 (junction area) to be at least 20% ofthe area of the p-type semiconductor layer 404 in the first embodiment.

Note that although the LED bare chips are mounted directly on the firstmain surface of the mounting substrate by flip chip mounting in FIG. 5,the LED bare chips may be mounted indirectly on the first main surfaceof the mounting substrate by a submounting method. An example of this isshown in FIG. 18. In the present invention, the LED bare chips may bemounted indirectly on the mounting substrate in this manner.

Specifically, FIG. 18 shows an example of a cross section of an LEDmodule in which the LED devices have been mounted on the mountingsubstrate indirectly. The following describes this in detail.

An LED module 30 in FIG. 18 is an LED mounting module that has the samestructure as that shown in FIG. 5. The LED mounting module includes thesubstrate 10 and a reflective plate 301. An LED bare chip 401 is mountedindirectly as a submount 40 on an LED mounting position of the LEDmounting module. Note that the LED module 30 includes a lens plate 302that is identical to that in FIG. 5.

The submount 40 is composed of, for example, a silicon substrate 409,the LED bare chip 401 which is mounted on the top surface of the siliconsubstrate 409, and phosphor 407 that envelopes the LED bare chip 401.Here, the LED bare chip 401 is mounted on the silicon substrate 409 viagold bumps G1, G2, and G3.

Note that a first electrode 408B, which is electrically connected fromthe p electrode 405 of the LED bare chip 401, is formed on the topsurface of the silicon substrate 409. Furthermore, an electrode 410,which is electrically connected from the first electrode 408B, is formedon the bottom surface of the silicon substrate 409. A second electrode408A, which is electrically connected to an n electrode 406 of the LEDbare chip 401, is also formed on the top surface of the siliconsubstrate 409.

In the present example, aluminium is used as the electrode material, andthe junction is a gold-aluminium junction. However, gold, tin, or alloysthereof may be used, and selected so that the junction is a gold-goldjunction or a gold-tin junction.

The submount 40 is mounted to the LED mounting-use module usingelectrically conductive paste (silver paste) 411. The submount 40 andthe substrate 10 are electrically connected by the electrode 410 on thebottom surface of the silicon substrate 409 being connected via thesilver paste 411 to the wiring patterns 201B formed on the substrate 10,and the second electrode 408A on the top surface of the siliconsubstrate 409 being connected via a wire 412 to the wiring pattern 201Aof the substrate 10.

Metal powder and resin are used for the electrically conductive paste.Other than silver, the metal powder may be one or more types selectedfrom the group consisting of copper, nickel, palladium, and tin, or analloy of one or more of the types.

When the LED bare chip 401 is mounted indirectly by submounting, thesubmount 40 that includes the phosphor 407 can be formed in advance, andtherefore, for example, it is possible to check whether the LED devicethat has been mounted on the silicon substrate illuminates normally.Consequently, the submount can be mounted on the LED mounting moduleafter being checked, and effects such as increased yield inmanufacturing can be obtained.

<Second Embodiment>

2-1. Structure of the LED Lighting Apparatus (Bulb-Type Lamp)

FIG. 10A shows the structure of an LED lighting apparatus of the secondembodiment. An LED lighting apparatus 100 shown in the drawing can beused as a general bulb-type lamp, and uses the LED card 1 having thestructure of the first embodiment shown in FIG. 1 as the light source.

As shown in the FIG. 10A, the LED lighting apparatus is roughly composedof a disc-shaped LED mounting unit 101, a main body 130, and ascrew-type terminal 140.

A card socket 110 which removably holds the LED card 1 described in thefirst embodiment is provided on the main surface of the LED mountingunit 101. The card socket 110 is connected to a main surface side of theLED 110 by a hinge 110 a, and is normally stored parallel to the mainsurface of the LED mounting unit 101, embedded therein. A user is ableto remove the LED card 1 by raising the card socket 100. Note thatterminals that are electrically connectable with the power terminals 20a to 20 h of the LED card 1 are provided in the card socket 110. Theseterminals supply the LED card 1 appropriately with power via a commonlyknown lighting circuit (not illustrated) housed in the main body 130.

The card slot 110 can be fabricated, for example, from a material suchas aluminium or cupronickel, which has superior heat dischargeproperties. Claws 101 a and 101 b provided of a side surface of the LEDmounting unit 101 can be used to attach a lamp shade 150.

As shown in the cross sectional drawing of the lighting apparatus inFIG. 11, the LED mounting unit 101 is provided internally with a base121 that is parallel to the main surface of the LED mounting unit 101and is directly below the card socket 110, and a heatsink 120 that is aheat dissipating means. The heatsink 120 has a plurality of fins 122that extend toward the inside of the main body 130, and is fabricatedfrom a material that has superior heat conducting properties such ascopper or aluminium. The base 121 of the heatsink 120 is disposed sothat the surface thereof is in close thermal contact with the metallayer 10 b of the LED card 1 mounted in the card socket 110.

Note that the material used for the heatsink may be one or more typesselected from the group consisting of Al, Cu, W, Mo, Si, AlN, and SiC.

A characteristic of the second embodiment is that the heatsink 120 hasan enveloping volume of at least 100 cm³, and its heat dissipatingability is a thermal resistance of at least 4.0° C./W.

2-2. Effects of the Heatsink of the Present Invention

According to the lighting apparatus 100 having the stated structure, thescrew-type terminal is mounted in a commonly known socket at the time ofuse. During driving, the LED light emitting unit 30 emits light at aluminous output of 1201 m, according to power of a maximum voltage of120 V to the LED card 1.

At this time, heat generated in the LED card 1 is favorably dissipatedfrom the substrate 10 by the heatsink 120 provided in close thermalcontact with the metal layer 10 a of the LED card 1. In the secondembodiment, since the heat dissipating ability of the heatsink 120 is athermal resistance of at least 4.0° C./W, the heat generated in the barechips 2 is effectively dissipated from the p electrode 405 through themetal layer 10 a to the heatsink 120 side, and the temperature emittedby the LED bare chips 2 is kept to 80C or lower. As a result, thermaldeterioration of the LED bare chips 2 can be prevented, superiorluminous efficiency can be achieved, and the lighting apparatus 100 canbe used as a favorable lighting apparatus.

2-3. Relationship Between LED Bare Chip Temperature and HeatsinkCharacteristics

The following describes information about the relationship between LEDbare chip temperature in the LED card 1 and heatsink characteristics,obtained by the inventors according to experiments. Note that LED chiptemperature is measured as the junction temperature at the p electrode.

FIG. 12 is a graph showing the relationship between bare chiptemperature and heatsink resistance. The graph shows the respectiveeffects of thermal resistance of the heatsink on the bare chiptemperature when the LED bare chip are driven with maximum currents of20 mA (5 W), 30 mA (6 W), 40 mA (9 W), and 50 mA (11 W). The lines inthe graph are drawn according to the respective relation expressionsindicated in the graph with respect to the lines.

The heat generated in the LED card during driving depends on the forwardcurrent in the making power and the thermal resistance of the heatsinkused. As described earlier, it is important to keep the drivingtemperature of the LED bare chips to 80° C. or below for reasons ofthermal deterioration and maintaining luminous efficiency. Consequently,it is necessary to select a heatsink for use in the LED lightingapparatus of the present invention that has the ability to keep heatemitted by the LED bare chips to 80° C. or below.

Referring at the graph with such a condition in mind, it can be seenthat when driving the LED bare chips with a maximum current of 50 mA,the LED bare chip temperature cannot be kept to 80° C. or lower if theheat sink thermal resistance is not sufficiently less than 5.0° C./W.Consequently, it is thought that choosing a heatsink with a thermalresistance of 4.0° C./W will enable the LED bare chip temperature duringdriving to be kept to substantially 80° C. or lower.

Since a making power with a maximum current of 50 mA is generallythought to be the upper limit for making power for driving LED barechips in an LED card, it is thought that the LED bare chip temperaturecan be kept to 80° C. or below if the thermal resistance of the heatsinkis 4.0° C./W or lower. These grounds form the basis for the use of aheatsink with a thermal resistance of 4.0° C./W or lower in the presentinvention.

FIG. 13 is a graph showing the relationship between bare chiptemperature and heatsink enveloping volume. This graph also indicatesresults for when the LED bare chips were driven with maximum currents of20 mA, 30 mA, 40 mA, and 50 mA, and shows the effect of heatsinkenveloping volume on bare chip temperature. The lines in the graph aredrawn according to the respective relation expressions indicated in thegraph with respect to the lines.

The graph shows that the LED bare chip temperature can be kept to 80° C.or below if the heat sink enveloping volume is 100 cm³ or greater. Fromthis is can be concluded that a heatsink having an enveloping volume of100 cm³ is preferable for use in the present invention. Taking intoconsideration the heatsink thermal resistance shown in FIG. 8 and theupper limit of the enveloping volume thereof, thermal resistanceproperties of no less than 1.0° C./W and no greater than 4.0° C./W canobtained if a heatsink having an enveloping volume of at least 100 cm³and no greater than 820 cm³ is used. This enables heat to be dischargedeffectively from the LED bare chips.

FIG. 14 is a graph showing the relationship between bare chiptemperature and heatsink surface area. This graph also indicates resultsfor when the LED bare chips were driven with maximum currents of 20 mA,30 mA, 40 mA, and 50 mA, and shows the effect of heatsink surface areaon bare chip temperature.

The graph shows that the LED bare chip temperature can be kept tosubstantially 80° C. or below if the heat sink if the area is at least acertain size. From this is can be concluded that a heatsink having aarea of at least a certain size is preferable for use in the presentinvention. Furthermore, if the surface area of the heatsink issufficiently large, the heat generated in the LED bare chips fallsgradually from around 50° C. and saturation occurs. Therefore, anunnecessarily large heatsink is not required in terms of reducing theheat generated in the LED bare chips.

FIG. 15 is a graph showing the relationship between bare chiptemperature and heatsink weight. This graph also indicates results forwhen the LED bare chips were driven with maximum currents of 20 mA, 30mA, 40 mA, and 50 mA, and shows the effect of heatsink weight on barechip temperature.

The graph shows that the LED bare chip temperature can be kept tosubstantially 80° C. or below the weight is at least a certain amount.From this is can be concluded that a heatsink having a weight of atleast a certain amount is preferable for use in the present invention.Furthermore, if the area of the weight of the heatsink is sufficientlylarge, the heat generated in the LED bare chips falls gradually andsaturation occurs. Therefore, an unnecessarily heavy heatsink is notrequired in terms of reducing the heat generated in the LED bare chips.

As described, it is clear that LED bare chip temperature changes due tofactors such as heatsink thermal resistance, enveloping volume, area,and weight. This means that the heatsink can be subject to variousquantative analytic evaluations according to the stated factors.

2-4. Other LED Lighting Apparatus Structures

The LED lighting apparatus is not limited to the structure described inthe second embodiment in which the LED card 1 is removable from the cardsocket 110. Furthermore, a plurality of LED cards 1 may be used in theLED lighting apparatus.

FIGS. 16A and 16B shows variations of the structure of the LED lightingapparatus of the second embodiment.

FIG. 16A shows the structure of a lighting apparatus 500 that is abulb-type lamp similar to the lighting apparatus 100 of the secondembodiment.

An LED mounting unit 501 of the lighting apparatus 500 a has slot unit510 instead of a card socket that is a separate member as in the secondembodiment. The slot unit 410 is provided as a channel in the surface ofthe disc-shaped LED mounting unit 501, and removably holds one of theLED cards 1. A lamp shade 550 can be provided on the periphery of theLED mounting unit 501. Furthermore, a screw-type terminal 540 that isconnectable with a commonly-known external socket is provided at thebottom of the main body 530.

With this structure, an LED card 1 provided on the LED mounting unit 501is in close thermal contact with a heatsink 520 provided inside the LEDmounting unit 501, in a similar manner to the second embodiment. Theheatsink 520 has a thermal resistance of 4.0° C./W or lower.

The three LED cards 1 are positioned evenly on the disc-shaped LEDmounting unit 501, the extra LED cards 1 meaning that a higher luminousoutput is achieved that that of the LED lighting apparatus 100 of thesecond embodiment. This structure achieves substantially the sameeffects as the second embodiment, with the heat generated in the LEDcards 1 being kept to 80° C. or lower.

Furthermore, FIG. 16B shows an example of a structure of a torch-typeLED lighting apparatus 600. This LED lighting apparatus 600 is roughlycomposed of an LED mounting unit 601, a grip unit 630, a switch unit640, and so on.

In this structure, the LED card 1 is removably mounted in a card slot610 formed on a surface of the LED mounting unit 601. When the LED card1 is in a mounted stated, the metal layer 10 a of the LED card 1 is inclose thermal contact with a heatsink 620 provided in the LED mountingunit 601. The heatsink 620 also has a thermal resistance of 4.0° C./W orlower. A battery or batteries are housed in the grip unit 630 as in acommonly-known torch, and power is supplied to the LED card 1 by thesliding switch unit 640 being operated.

This LED lighting apparatus 600 having a torch-type structure achievessubstantially the same effects as the second embodiment, with the heatgenerated in the LED cards 1 being kept to 80° C. or lower.

2-5. Heatsink Variations

The heatsink used in the present invention is not limited to theheatsinks 120, 520 and 620, which have a plurality of fins on a base,disclosed in the second embodiment and the variations.

FIGS. 17A, 17B and 17C show other heatsink structures.

FIG. 17A shows the structure of a heatsink that has a plurality of thickribs provided on a plate-shaped base. This structure is basically thesame as the heatsinks 120, 520, and 620 described in the secondembodiment and the variations, but the thickness and number of the finsis able to be appropriately adjusted. Adjusting these devices enables,for example, the surface area of the heatsink to be set.

FIG. 17B shows the structure of a heatsink that has a plurality of thin,square-shaped prongs provided on a plate-shaped base. This shape ofheatsink is generally used as a heat dissipating means for the CPU of apersonal computer, but may be used as the heat dissipating means for theLED card 1 of the present invention.

FIG. 17C shows the structure of a heatsink that has a plurality ofdisc-shaped bases provided with intervals there between and a columnconnecting the center of each base. In this structure each base is alsoa fin. The LED card 1 is put in close thermal contact to the bottombase. This structure is advantageous in that factors such as the thermalresistance, enveloping volume, area, weight, and so on of the heatsinkthat determine heat dissipating properties can be easily set byincreasing the number of bases provided.

Note that other heatsinks, such as one that includes a heat pipe, may beused. Furthermore, the heatsink may be used in combination with a forcedcooling device such as a fan, a water-cooling device, a Peltier device,or a self-vaporizing heatsink.

<Other Remarks>

The card-type LED module disclosed in the embodiments may be used as alight source in an apparatus other than an LED lighting apparatus. Asone example, the LED module may be used as a light source in a device,such as a display device, that requires highly luminous light emission.

INDUSTRIAL APPLICABILITY

The present invention may be used in lighting fixtures and lightingapparatuses that require a compact, thin or light-weight light source.

1. An LED lighting source comprising: a mounting substrate having awiring pattern on a first main surface thereof; and a plurality of LEDbare chips, each composed of a first semiconductor layer and a secondsemiconductor layer that have respectively different conductivity, anactive layer disposed between the first and second semiconductor layers,and a metal electrode disposed on the first semiconductor layer andbeing substantially equal in area to the first semiconductor layer, andeach LED bare chip being joined to the wiring pattern according to flipchip mounting of the metal electrode to form a junction between thewiring pattern and the metal electrode, wherein each junction is formedso that an area thereof is at least 20% of the area of the metalelectrode, and thermal resistance from the active layers through to asecond main surface of the mounting substrate, which is a back surfacethereof, is set to 3.0° C./W or lower.
 2. The LED lighting source ofclaim 1, wherein at least the metal electrodes disposed on the firstsemiconductor layers and the wiring pattern are joined according to oneof a gold-gold junction, a gold-aluminium junction, and a gold-tinjunction.
 3. The LED lighting source of claim 1, wherein each junctionbetween the metal electrodes disposed on the first semiconductor layerof each LED bare chip and the wiring pattern is made up of two or morebumps.
 4. The LED lighting source of claim 1, wherein each junctionbetween the metal electrodes disposed on the first semiconductor layerof each LED bare chip and the wiring pattern is made up of two or morebumps that each have a diameter of at least 100 μm, or three or morebumps that each have a diameter of at least 80 μm.
 5. The LED lightingsource of claim 1, wherein current density of the active layer of eachLED bare chip during driving is in a range of 250 mA/mm² to 660 mA/mm²inclusive.
 6. The LED lighting source of claim 1, wherein the mountingsubstrate is composed of an insulation layer and a metal layer, thefirst main surface on which the wiring pattern is disposed being a mainsurface of the insulation layer, and the second main surface of themounting substrate, which is an opposite surface to the surface on whichthe wiring pattern is disposed, being a surface of the metal layer. 7.The LED lighting source of claim 1, wherein the mounting substrateincludes an insulation layer that is composed of a composite materialthat includes an inorganic filler and a resin composite.
 8. The LEDlighting source of claim 1, wherein the mounting layer includes aninsulation layer that is composed of a ceramic material.
 9. The LEDlighting source of claim 1, wherein the mounting substrate is composedof a ceramic material.
 10. The LED lighting source of claim 9, whereinthe ceramic material includes at least one of AlN, Al₂O₃, and SiO₂. 11.An LED lighting apparatus comprising the LED lighting source of claim 1,wherein the LED lighting apparatus includes a heats ink that is providedin close thermal contact with the back surface of the mountingsubstrate, and that has a thermal resistance of no less than 1.0° C./Wand no greater than 4.0° C./W.
 12. The LED lighting apparatus of claim11, wherein the heatsink is composed of at least one material chosenform the group consisting of Al, Cu, W, Mo, Si, AlN, and SiC.
 13. An LEDlighting apparatus comprising the LED lighting source of claim 1,wherein the LED lighting apparatus includes a heats ink that is providedin close thermal contact with the back surface of the mountingsubstrate, and that has an enveloping volume of 100 cm³ to 820 cm³,inclusive.
 14. The LED lighting apparatus of claim 13, wherein theheatsink is composed of at least one material chosen form the groupconsisting of Al, Cu, W, Mo, Si, AlN, and SiC.
 15. An LED lightingapparatus comprising the LED lighting source of claim 1, wherein the LEDbare chips are mounted to the mounting substrate by each LED bare chipbeing joined with a submount according to flip chip mounting, and eachsub-mount being electrically joined with the wiring pattern on the firstmain surface of the mounting substrate.
 16. An LED lighting apparatuscomprising the LED lighting source of claim 15, wherein the submountsand the mounting board are joined by conductive paste.
 17. An LEDlighting apparatus comprising the LED lighting source of claim 16,wherein the conductive paste is composed of (i) at least one materialselected from the group consisting of silver, copper, nickel, palladium,and tin; or an alloy that includes one of the materials, and (ii) one ofthe materials mixed with resin.